1. Field of the Invention
The present invention relates to an analyzer for analyzing the foreign matter on a semiconductor wafer or on the pattern of a semiconductor device formed on the semiconductor wafer, a control apparatus for controlling the manufacturing process of the semiconductor devices, a method for analyzing the foreign matter on the devices and a method for controlling the manufacturing process as applied to the analyzer and control apparatus.
2. Description of the Related Art
The minute foreign matter which adheres to a semiconductor wafer or to the pattern of a semiconductor device formed on a semiconductor wafer (including the foreign matter below the thin film formed on a semiconductor wafer) is a major factor in the low yield of the manufacturing process of semiconductor devices such as IC's or LSI's. In order to prevent the foreign matter from adhering to the wafer, it is important to identify the source of the foreign matter, and to take measures to prevent pollution. It is therefore necessary to analyze the composition ratio and the condition of the foreign matter.
Electron Probe Microanalysis (EPMA) using a Scanning Electron Microscope (SEM) is one of the conventional methods for such analysis. EPMA is also called X-Ray Microanalysis (XMA) in Japan.
The EPMA technique was developed in the latter half of the 1960's. It applies an electron beam to a test piece so as to detect characteristic X-rays which are generated from the foreign matter on the surface of the test piece, thereby identifying the composition ratio of the foreign matter. EPMA was described in detail in, for example, Takashi Kawahigashita's "Handoutai Hyoka Gijutsu (Semiconductor Evaluation Technique)", pg. 166-172, Sangyo-Tosho, and Akira Usami's "100 Rei ni Miru Handoutai Hyoka Gijutsu (Semiconductor Evaluation Techniques: 100 cases). There are two types of EPMA, i.e., wavelength dispersive type and energy dispersive type. The Energy dispersive type is superior to the wavelength dispersive type in both through-put and simplicity. Data as measured by energy dispersive type EPMA is described below.
FIG. 16 illustrates a typical secondary electron image by SEM in which two pieces of foreign matter A and B are adhered to the surface of semiconductor wafer 101. In the EPMA method, the foreign matter to be analyzed is indicated on the display in advance. Then, an electron beam is focused on and applied to the each bit of foreign matter respectively. The X-ray spectrum radiated by the foreign matters are displayed and analyzed respectively.
FIG. 17 illustrates a typical EPMA analysis spectrum of the foreign matter A. In this figure, the horizontal axis indicates X-ray energy the units of which are electron volts and the vertical axis indicates X-ray intensity the units of which unit are counts per second (CPS). The graph in this figure has a first peak of X-ray intensity I.sub.1 at X-ray energy E.sub.1 and a second peak of X-ray intensity I.sub.2 at X-ray energy E.sub.2. The first peak indicates that element X is contained in foreign matter A. The second peak indicates that element Y is also contained in foreign matter A. I.sub.1 and I.sub.2 are in a ratio of approximately 2:1. Thereby, FIG. 17 indicates that the composition ratio of elements X and Y in foreign matter A is approximately a 2:1 ratio, though the relationship between X-ray intensity and the composition ratio does not always have linearity because of various compensations.
FIG. 18 indicates a typical EPMA analysis spectrum of foreign matter B. The graph in this figure has a first peak of X-ray intensity I.sub.2 at X-ray energy E.sub.3 and a second peak of X-ray intensity I.sub.2 at X-ray energy E.sub.3. The first peak indicates that element Z is contained in foreign matter B. The second peak indicates that element Y is also contained in foreign matter B. The height of the first peak is approximately the same as the height of the second peak. Thereby, FIG. 18 indicates that the composition ratio of elements Z and Y in foreign matter B is approximately a 1:1 ratio.
Thus, on the basis of FIG. 17 and FIG. 18, the composition ratio and the element type of the elements which compose foreign matter A and B can be obtained. Based on these results, an analyst can identify what type of foreign matter A and B are. If the type is identified, the generation process of the foreign matters can also be identified.
As mentioned above, according to conventional methods of foreign matter analysis, an analyst obtains the composition ratio and the element type of the elements which composes the foreign matter based on spectral analysis, thereby identifying the type of foreign matter directly.
However, as the types of foreign matter adhering to a test piece increases, the types and the composition ratio of the elements which compose the foreign matter become much more varied. Consequently, according to the conventional methods of foreign matter analysis, data is very complex and thus difficult to explain. Also, it is very difficult to find the generation process of the foreign matter.
Thus, the conventional methods of foreign matter analysis have a low through-put and require a great deal of time and the skilled valuation of an analyst.